The brains of the chair.I responded to a summer job offer (thanks to a lead from the Maslab Robot project!) to work at Panasonic Boston Laboratory doing robotics research. It turns out that an engineer there just wanted to see if he could find an intern to whip up a cool robotic wheelchair to help severely disabled people navigate their homes. He wanted it done over the course of a few months, which is the length of a typical summer internship at Panasonic. I had my doubts about the timeline, but I was still happy to take him up on the offer. We set a few long term goals, threw out a number to use as a budget limit, and starting buying parts.
Linux SBC and motor controller.The wheelchair started as a Jazzy Powerchair. I stripped the heavy lead-acid car batteries in favor of some smaller gel cell batteries. It had really powerful gearmotors, but I dropped the voltage down to 12v to extend the battery life and make things a bit safer. The joystick interface looked pretty cryptic, so I ordered a Roboteq motor controller to wire up to the single board computer running Linux. One of the project goals was to make every wheelchair modification easy to replicate. I had a rudimentary picture of design for manufacture in mind. We had a steel frame welded at a local shop. It contained the batteries, computer, motor controller, and power supplies. I ended up with a nice, self-contained "power box" suitable for running anything from a wheelchair to a Battlebot. The entire frame lowered directly into the space where the two large car batteries once lived.
The "power box".One of my favorite sensors for use in robotics is the SICK Lidar, but that just didn't make sense for a project liek this. Few people could afford the extra $6K for that kind of sensor. I chose analog infrared sensors with a range of about one meter and sonar sensors with a range of several meters. I ordered eight of each sensor and wired them to give close to 360 degree coverage of the perimeter of the wheelchair.
I also used this project as an excuse to dive into basic machine vision. I played with stereoscopic cameras for a while when working on the DARPA Grand Challenge project, but in this case a simple webcam like the QuickCam Pro 5000 worked fine. In fact, I enjoyed writing software for the webcam under linux so much that it spawned an entire open source robotics library. Anyways, I didn't get too far with the camera other than writing an extensive library for it and doing a couple basic demos. I did get the wheelchair to follow around anyone wearing red, which basically halted all productivity at Panasonic Boston Laboratory for at least an hour.
Custom sensor processing board.As usual, I chose to build my own sensor processing electronics for this project. It would have made more sense to just buy a USB data acquisition board off the shelf, but I enjoy making those kinds of boards, and it's always a great learning experience. This one used an ATMEGA128 to read the sensors and communicate with the Linux SBC. My supervisor also had some data-logging projects in mind, so he had me add a few connectors and write software for several other sensors. It ended up supporting temperature sensors, thermocouples, flow meters, and some weird light sensor. It turned out to be a very useful board, but it probably wasn't worth the week it took to design the pcb and write software and firmware for everything.
It was good at finding orange.The robot wheelchair exclusively used code from my Open Source Robot Controls library. It seemed clear to me that the code I was writing would be very useful to others, and I was right. I've heard from several people who have taken snippets of my code for their own projects. In fact, the MIT's iCampus robotic tour guide uses quite a bit of code that was originally written for this wheelchair. I had extensive plans to do sonar based mapping and scan matching, fiducial recognition, and voice command, but unfortunately I just ran out of time.
Everything is hidden.Panasonic generously agreed to donate my wheelchair project to the student-run robotics lab sponsored by MIT's Edgerton Center. I've been heavily involved in the group's projects so far. We've entered the DARPA Grand Challenge with about $80K worth of robotic pickup truck and we're currently building a $30K robot to give tours to prospective MIT students. In short, I think this was probably the best thing that could have happened to this project. I hope you liked the pictures.
If anyone at MIT is reading this, let me know if you have a good use for this robot. Right now we're using it as a test platform for Lidar algorithms, but if your lab group could use something like this I'd be glad to consider it. Otherwise this thing is just going to turn into a drink server...
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